The present invention relates to capacitor structures and to magnetic circuits employing capacitive elements.
The paradigm of capacitor structures is that in which at least a pair of conductive sheets or plates are adjacently disposed with at least one layer of dielectric material between them. In such structures, alternate plates or layers are often connected by means of a common electrical lead so as to form a device exhibiting a certain capacity per unit volume. In general, the capacitance of such a perma structure is governed by its geometry and the electrical permittivity of the dielectric material between the plates. More particularly, the capacitance is generally linearly proportional to the area of the plates employed and inversely proportional to the separation distance between the plates. Nonetheless, in known prior art capacitor structures, the requirement for at least a pair of electrically-insulated and separate conductors has been present.
The construction of multi-stage filters is also generally well known in the electrical arts. In particular, the construction of inductor-capacitor (LC) multi-stage, low pass filters is well known. Such filters generally are often configured in a ladder network in which capacitive elements are employed as the rungs, or shunt elements, of the circuit. Similarly, inductive elements are generally employed as the series elements in such circuits. These circuits are particularly useful in inverter applications in which a direct current signal is "chopped" into a plurality of rectangular pulse-like signals for passage through and control by inductive circuit elements. The high speed chopping circuit often, however, introduces unwanted high frequency signal components. It is the low pass filters mentioned above which are particularly useful in eliminating, or at least mitigating, the effects of these high frequency components. In such inverter circuits, particularly those employed in electronic discharge lamp ballast configurations, it is also desirable that the overall circuit configuration be small, compact and light-weight. It is therefore desirable to be able to integrate as many components as possible into as few structures as possible.
In application Ser. No. 292,322, filed in 1981, titled "Integrated Transformer and Inductor", the instant inventor teaches that the use of gapped legs in magnetic core circuits can effectively provide inductive components for filter circuits, particularly filter circuits such as are considered herein. Accordingly, because of these teachings, the aforementioned application is hereby incorporated herein by reference. Furthermore, in U.S. patent application Ser. No. 243,324, titled "A Ballast Circuit For Driving a Plurality of Fluorescent Lamps", the instant inventor also teaches that integrated magnetic circuits having gapped legs are employable in ballast circuits for fluorescent lamps. Accordingly, because of related teachings therein, the aforementioned patent application is also incorporated herein by reference. However, in these two prior submitted applications, it is to be noted that in each case, the capacitive elements are provided in the same manner. That is to say, in each case a separate and distinct capacitance is provided by employing a conventional capacitor connected across the winding disposed on an appropriate portion of the transformer core. In the present invention, this winding and capacitive element are integrated into a single structure. This structure is lower in cost since the winding required for coupling the capacitor to the magnetic structure is eliminated. The structure of the instant invention is also unique in that connection of conventional leads is not required. In spite of the apparently intuitive notion that such a device will not operate as a capacitor since no external electrical connections are provided and since there is only a single conductive sheet, nonetheless the present invention acts as a conventional capacitor when used in connection with a magnetic structure.